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Über dieses Buch

The Internet plays a significant and growing role in real-time industrial manufacturing, scheduling and management. A considerable research effort has led to the development of new technologies that make it possible to use the Internet for supervision and control of industrial processes.

Internet-based Control Systems addresses the challenges that need to be overcome before the Internet can be beneficially used not only for monitoring of but also remote control industrial plants. New design issues such as requirement specification, architecture selection and user-interface design are dealt with. Irregular data transmission and data loss and, in extreme cases, whole-system instability may result from Internet time-delay; this book guards against such phenomena from both computer science and control engineering perspectives. Security breaches and safety risks in an Internet-based control system could have very serious consequences and the author gives specific advice for avoiding them. This book is unique in bringing together multiple strands of research, mainly from computer science and control engineering, into an over-arching study of the entire subject.

Practical perspectives are explored both through case studies in several chapters and through real applications including:

· robot arm control;

· web-based simulator for a catalytic reactor;

· virtual supervision parameter control of a water tank system;

· model predictive control for a process control unit;

· remote control performance monitoring and maintenance;

· remote control system design and implementation;

Internet-based Control Systems is a useful introduction and guide for researchers in control engineering and computer science and developers of real-time Internet-enabling software. It can also be used for teaching a final year option or elective on Internet-enabled real-time system design, or as an advanced example of real-time software design for graduates.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

This chapter firstly introduces the concepts of and the difference between control over a network and control of a network. As a special type of networked control system, Internet-based control systems use the Internet as the shared communications network and bring the Internet into the control loop as a control system element. In both networked control systems and Internet-based control systems, there are a number of common challenges that must be faced. This chapter highlights these challenges and this book as a whole aims to provide the solutions to these challenges.
Shuang-Hua Yang

Chapter 2. Requirements Specification for Internet-based Control Systems

This chapter describes an approach to writing requirements specifications for Internet-based control systems and to deriving architectures for this new type of control system according to the requirements specification. The specification is described in terms of a functional model and then extended into an information architecture. Distinct from the functional model, the information architecture gives an indication regarding the architecture of the Internet-based control systems. An integrated–distributed architecture has been derived as an ideal implementation, in which the control system is linked with the Internet at all levels in the control system hierarchy.
Shuang-Hua Yang

Chapter 3. Internet-based Control System Architecture Design

This chapter introduces the various control system architectures that can be used for remote control and monitoring. The traditional bilateral teleoperation is used to illustrate the generic concept of tele-operation. The structure of remote process control over the Internet is derived from the generic process control system hierarchy by adding an extra Internet layer above. Three canonical Internet-based control system structures are given, with the operator located remotely, the controller located remotely, or with bilateral controllers.
Shuang-Hua Yang

Chapter 4. Web-based User Interface Design

There are two questions to be answered in the user interface design for Internet-based control systems: how information should be displayed to the remote operator on the control system user interface and what information should be displayed. Multimedia interface design has been used to answer the first question in this chapter. We do not investigate the second question in our study and believe that formal methods may be able to provide the answer to it (Hussak and Yang, International Journal of Automation and Computing 4(4):413–421, 2007).
Shuang-Hua Yang

Chapter 5. Real-time Data Transfer over the Internet

Efficient real-time data exchange over the Internet plays a crucial role in the successful application of Internet-based control. In this chapter, a data transfer mechanism over the Internet is introduced for real-time web-based applications, particularly for Internet-based control systems. The mechanism incorporates the eXtensible Markup Language (XML) and Hierarchical Data Format (HDF) to provide a flexible and efficient data format. Heterogeneous transfer data are classified into light and heavy data, which are stored using XML and HDF, respectively; the HDF data format is then mapped to Java Document Object Model (JDOM) objects in XML, in the Java environment. These JDOM data objects are sent across computer networks with the support of the Java Remote Method Invocation (RMI) data transfer infrastructure. Clients defined data priority levels are implemented in RMI, which guides a server to transfer data objects at different priorities. A remote monitoring system for an industrial reactor process simulator is used as a case study to illustrate the proposed data transfer mechanism.
Shuang-Hua Yang

Chapter 6. Dealing with Internet Transmission Delay and Data Loss from the Network View

The biggest obstacles in the design and implementation of Internet-based control are the Internet transmission delay and data loss. There are two ways to deal with this issue: one is from the network infrastructure perspective and the other is from the control system structure design and compensation algorithms perspective. This chapter addresses the time delay and data loss issue only from the network infrastructure viewpoint. Firstly, six requirements for an ideal network infrastructure are proposed, followed by a description of the features of Internet communication. In order to meet the requirements of real-time data transmission, a combined network infrastructure is investigated, which integrate The Transmission Control Protocol, User Datagram Protocol, Real-time Control Protocol, and the Network Time Protocol. The advantages of each transmission protocol have been used in the integrated infrastructure with the elimination of their weak features.
Shuang-Hua Yang

Chapter 7. Dealing with Internet Transmission Delay and Data Loss from the Control Perspective

Following on from the previous chapter, Chap. 7 describes how to deal with Internet transmission delay and data loss from the viewpoint of both the control system structure and compensation algorithms. Five control system structures are presented here: virtual supervision parameter control, model-based predictive display tele-operation, intelligent autonomy control, control system with a variable sampling time, and multi-rate control. Feedback and feed-forward time delay compensator design is also described in detail. A compensator located at the feedback channel is designed to overcome the time delay that occurs during the transmission from the local site to a remote site. Another compensator, in the feed-forward channel, is designed to compensate for the time delay occurring in the control action transmission. Simulations and experimental studies that focus on the virtual supervision parameter control, control with a variable sampling time, and multi-rate control with time delay compensation structures are described. They are designed for various requirements. The multi-rate control scheme presented with the time delay compensators offers a promising way to efficiently reduce the effect of Internet time delay on control performance, in which a two-level hierarchy is used. At the lower level, a local controller is implemented to control the plant at a higher frequency. At the higher level, a remote controller is employed to remotely regulate the desirable setpoint at a lower frequency for the local controller.
Shuang-Hua Yang

Chapter 8. Design of Multi-rate SISO Internet-based Control Systems

This chapter presents a design method for multi-rate Internet-based control systems to achieve load minimization and dynamic performance specifications in a single-input and single-output system. It avoids the complexity of large-scale system design by focusing on individual control systems. In the multi-rate control scheme described in the previous chapter, the plant under control is first stabilized by a local controller with a high sampling rate. The remote controller, which regulates the output according to the desirable reference, adopts a low sampling rate to reduce load on the network. In this chapter, the upper bound of the remote controller’s sampling interval, which meets the requirement on control performance, is derived and a simple tuning method when the remote controller is chosen as a PID is presented. Simulation and experiemental studies are provided for illustration.
Shuang-Hua Yang

Chapter 9. Design of Multi-rate MIMO Internet-based Control Systems

This chapter discusses the state feedback control for multi-rate multi-input and multi-output Internet-based control systems. We firstly formulate a dual-rate control system with Internet time delay at both feedback and feed-forward channels and design a state feedback controller for the system. The asymptotic stability is then investigated. A necessary and sufficient criterion for asymptotic stability for such dual-rate control systems is established. Compensation for random transmission time delay at both feedback and feed-forward channels is presented, in which a state-space process model with a local controller is implemented in the remote control node and a buffer is located in the local control node. A simulation example is given to illustrate the effectiveness of the time delay compensation.
Shuang-Hua Yang

Chapter 10. Safety and Security Checking

Internet-based control systems use the Internet as the communication medium to enable the remote monitoring and control of plants and to initiate global collaboration and data sharing between operators from geographically dispersed locations. However, connection to the Internet presents high safety and security risks to this new generation of control systems. Are we opening up our Internet-based control systems to trouble since a number of malicious hackers continually attack Web servers on the Internet? The new type of control systems will never be accepted by industry, if people do not have enough confidence in their safety and do not feel secure while using the system. This chapter presents a framework for security and safety checking used in the design of Internet-based control systems, which focuses on the security of control commands transferred over the Internet, actions to respond to malicious attacks, and system safety. The Internet-based control system introduced in Chap. 8 has been used as a case study to illustrate the implementation of the framework.
Shuang-Hua Yang

Chapter 11. Remote Control Performance Monitoring and Maintenance over the Internet

The Internet provides an ideal platform for remote performance monitoring and maintenance of real-time control systems. This chapter introduces the need for and objectives of remote performance monitoring and develops a systematic method for the design of such a remote monitoring and maintenance system, specifically for process control systems. A back-end and a front-end architecture are proposed for the remote performance monitoring and maintenance of control systems, in which all the heavy calculations are carried out locally, while light data and the characteristics of any heavy data are sent to the front end located on the remote side for consideration by remote experts. The remote control performance monitoring and maintenance system is illustrated by reference to the implementation in a process control unit.
Shuang-Hua Yang

Chapter 12. Remote Control System Design and Implementation over the Internet

This chapter describes an approach to the design, testing, and implementation of real-time control systems over the Internet. Process models and control systems are remotely designed and tested in a virtual environment and then implemented in a real plant through a distributed integration environment. Although the system designers and real-site operators are geographically dispersed, they work together as a team over the Internet without any effect caused by the distance between them. As a consequence, both time and money can be saved because there is no need for any control software supplier’s expert to travel to the site of the real plant and conduct on-site implementation. A generic control system life cycle model is presented first in this chapter. An Internet-based distributed general information infrastructure is proposed and implemented to remotely facilitate process modeling, control system design, simulation, validation, and on-site implementation. A water tank rig with a liquid level control system is used as a case study to illustrate how the remote design, testing, and implementation over the Internet are implemented in the distributed integration environment. Although service-oriented architecture, distributed data service, and Jini technologies are three possible options for implementing the integrated environment, only the Jini technology is used here.
Shuang-Hua Yang

Chapter 13. Conclusion

This chapter summarizes the findings, identifies the issues that have not been addressed in the book, and lists some directions for future research. The main conclusion is that the Internet provides a superb platform for the remote design, monitoring, control, and maintenance of real-time control systems, but many issues still need to be properly addressed, such as the control system specification, architecture, interface design, time delay compensation, and security and safety. It is hard to find generic solutions for some issues. Therefore, application-specific solutions have to be provided. This book provides systematic solutions to Internet-based control systems design and applications for both control engineering and computer science perspectives.
Shuang-Hua Yang

Backmatter

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